EAETHQUAKES ON THE PACIFIC COAST 7 



U. S. Naval Observatory at Mare Island, and since this date, there- 

 fore, there is more likelihood that the times in this catalogue are 

 accurate. Third, the place or places where the shock has been 

 felt. Here the abbreviation " S. F." stands for San Francisco. 

 Wlien necessary the name of the county is added for convenience. 

 Fourth, the intensity of the shock, expressed either in common 

 language or in terms of some arbitrary scale. Professor Rockwood, 

 in indicating the intensity, has used the adjectives: 1, very light; 

 2, light; 3, moderate; 4, strong; 5, severe; 6, destructive; but has 

 added a Roman numeral to indicate the intensity, according to 

 the Rossi-Forel scale, adopted by Swiss and Italian seismologists. 

 In Professor Rockwood's papers, very light is II or III; light, IV; 

 moderate, V or VI; strong, VI or VII; severe, VIII; destructive, 

 IX or X. 



Fifth — A brief reference to the source of information, so that 

 in nearly all cases the original record can be consulted, if desired. 

 Exceptionally heavy shocks, such as those of 1865, 1868 and 1872, 

 are treated with much more fullness than the lighter ones. 



I strongly recommend the use of the Rossi-Forel scale, on account 

 of the definiteness of the classification and because of the compara- 

 tive regularity of the gradations. In order to make it better known 

 in California, I reprint it here: 



The Rossi-Fokel Scale.* 



Microseismic shock — recorded by a single seismograph, or by 

 seismographs of the same model, but not putting seismographs of 

 different patterns in motion; reported by experienced observers 

 only. 



*First proposed by Rossi in Archives den Sci. Phys. et Nat., IV, p. 'Sl\ (1880), 

 and quite independently by Forel, ibid., VI, p. 461. After comparing hun- 

 dreds of published accounts of California earthquakes, I have found that the 

 words here printed in italics (which form no part of the Rossi-Forel scale as 

 proposed by its authors) are frequently employed by California observers. 

 They are here printed for convenience. When any one is describing the effect 

 of a shock he should employ the numerals I, II, III, etc., of the Rossi-Forel 

 scale. When, on the other hand, one is reading an account of a California 

 earthquake and seeking to assign the proper R.-F.. numeral, it will be found 

 that the words here set down in italics are of service. 



